<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>JS打字小游戏</title>
    <style>
        body {
            padding: 0px;
            margin: 0;
        }

        #gameStage {
            width: 100%;
            height: 1000px;
            background-color: aquamarine;
        }
    </style>
</head>
<body>
<div id="gameStage"></div>
<script>
  /**
   * 字母
   * @param id
   * @param alphabet
   * @param posX
   * @param posY
   * @param size
   * @constructor
   */
  function Word(id, alphabet, posX, posY, size) {

    //初始化数据
    this.id = id || '';
    this.alphabet = alphabet || 'a';
    this.posX = posX || 0;
    this.posY = posY || 0;
    this.size = size || 64;
    this.speed = 5;


    // 新建
    this.create = function () {
      var str = '<span class="word" id="alphabet-' + this.id + '">' + this.alphabet + '</span>';
      var gameStage = document.getElementById('gameStage');
      gameStage.innerHTML += str;

      var divNode = document.getElementById('alphabet-' + this.id);
      divNode.style.position = 'absolute';
      divNode.style.fontSize = this.size + 'px';
      divNode.style.left = this.posX + 'px';
      divNode.style.top = this.posY + 'px';
      
      this.speed = Math.floor(Math.random() * 20) + 5;
    };

    // 移动到指定点
    this.moveTo = function (posX, posY) {
      this.posX = posX;
      this.posY = posY;

      var divNode = document.getElementById('alphabet-' + this.id);
      divNode.style.left = posX + 'px';
      divNode.style.top = posY + 'px';
    };

    this.remove = function(){
      var divNode = document.getElementById('alphabet-' + this.id);
      divNode.remove();
    };
  }

  /**
   * 导演类
   */
  var director = {
    alphabets: ['A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z'],

    nodes: new Array(),

    /**
     * 逐帧运行
     */
    runFrame: function () {
      //更新已经产生所有点的坐标
      for (var index in this.nodes) {
        var node = this.nodes[index];
        if (node) {
          node.moveTo(node.posX, node.posY + node.speed);
          if (node.posY > 600){
            node.remove();
            this.nodes.splice(index, 1);
          }
        }
      }

      //随机产生字母
      var r = Math.floor(Math.random() * this.alphabets.length);
      var w = new Word(new Date().getTime(), this.alphabets[r]);

      w.create();
      this.nodes.push(w);

      var posX = Math.floor(Math.random() * window.innerWidth);
      if (posX < 50) {
        posX = 100;
      }
      if (posX >= window.innerWidth - 100) {
        posX = window.innerWidth - 100;
      }

      w.moveTo(posX, 0);
    },

    /**
     * 开始游戏
     */
    start: function () {
      var str = '<span class="word" id="score">' + 0 + '</span>';
      var gameStage = document.getElementById('gameStage');
      gameStage.innerHTML += str;

      var divNode = document.getElementById('score');
      divNode.style.position = 'absolute';
      divNode.style.fontSize = 64 + 'px';
      divNode.style.left = 800 + 'px';
      divNode.style.top = 800 + 'px';


      var _this = this;

      //监听键盘事件
      document.onkeydown = function () {
        var alphabet = String.fromCharCode(event.keyCode); //获取键盘敲中的字母
        var bCodeFound = false;
        for (var i = 0, len = _this.nodes.length; i < len;) {
          if(!_this.nodes[i]) {
            break;
          }
          if (alphabet === _this.nodes[i].alphabet) {
            _this.nodes[i].remove();
            _this.nodes.splice(i, 1);
            bCodeFound = true;
          }
          else {
            ++i;
          }
        }

        if (bCodeFound){
          scoreCounter.incScore();
        }
        else {
          scoreCounter.desScore();
        }

        var divNode = document.getElementById('score');
        divNode.innerText = scoreCounter.getScore();
      };

      //游戏主循环
      setInterval(function () {
        _this.runFrame();
      }, 200);
    }
  }

  /**
   * 计分器
   */
  var scoreCounter = {
    score: 0,
    incScore: function () {
      this.score++;
    },
    getScore: function () {
      return this.score;
    },
    desScore: function() {
      this.score--;
    }
  };


  director.start();

</script>
</body>
</html>